Causal modelling has been used to analyse various quantum phenomena. For example, one significant result in this framework is due to Wood and Spekkens[1]}, who showed that any classical causal model which reproduces the Bell correlations must be `fine-tuned' in the sense that the underlying causal model postulates causal connections between events which appear causally unconnected at the level of the empirical statistics. To see how this works, note that the proof of the Bell inequality can be regarded as telling us that any causal model for correlations violating the Bell inequality must postulate a causal connection between the choice of measurement on one particle and the outcome of the measurement on the other particle, but the quantum mechanical no-signalling theorem ensures that at the statistical level there will be no dependence of the outcome on the measurement choice, so if we wish to represent these statistics by a causal model we must carefully `fine-tune' the parameters of the model to ensure that the underlying causal influences exactly cancel out so as to be invisible at the level of the empirical statistics.
